I met a problem while I am generating 3D mesh using the version of 2.05. The error is an input error telling me that I have BND_FACES or BND_QUADS missing. I really have no idea how to solve this and hope you can help me. The screenshot below shows the detail about the error and I also attached my work.

This error message means that the surface mesh (input mesh for the 3D mesh generator) is incorrect and some boundary faces are missing. This is probably caused by insufficient density of the 2D mesh, i.e. incorrectly defined mesh refinements. I see that you are trying to refine the mesh on the pipe using some lines but note that these line are not integrated in any solid and has no influence on the mesh. Also the mesh refinement #5 on Solid 2 is quite wrong and was probably intended for Solid No. 11. I fixed your mesh refinements, which solved the original problem (the fixed project is attached) but there is another problem with very sharp angles and almost zero-thickness of some solids(see pictures below). The mesh optimization for your domain is not a trivial task and can take several hours, which is out of the range of free support.
Mirek

I am also doing 3D modelling on my project and now i got the same problem. I Red problem description and suggestion but i could not identify how to solve it in my model. Could anyone help me to detect the exact reason on my model and how can i solve it. I really want to learn how to identify the problem and solve it. I tried to reduce and increase the mesh size and mesh refinement but it did not work.

The problem is in incorrectly defined boundary of solid V2. See the selected surfaces in the attached screenshot - these surfaces are boundaries of solids V3 and V4, which are "internal solids" of solid V2. This is OK, since both solids indeed lie inside solid V2 and do not touch its boundary. However, in such a case surfaces 11,12,15-26 should not be defined explicitly as boundary surfaces of V2 (this "boundary" is created automatically from "internal solids"). The solution is to remove surfaces 11,12,15-26 from the list of boundary surfaces of Solid 2, i.e. the correct list of boundary surfaces is 1,5-10,13,14,27-34. You will also have to increase the maximum number of mesh-nodes, since your mesh will have almost 600k mesh nodes and about 1.5 mil. FE. Attached is the fixed project.
M.

Dear Mirek,
Thanks for your reply with detailed explanation. I followed your advice and it really solve the problem. I know that my biggest mistake was to use the boundary surfaces of the internal solids as boundary surfaces for solid 2.